Systems and methods for a semiconductor structure having multiple semiconductor-device layers

Abstract

A method of fabricating a semiconductor structure having multiple semiconductor device layers is provided. The method comprises providing a bulk substrate and growing a first channel material on the bulk substrate wherein the lattice constant of the first channel material is different from the lattice constant of the bulk substrate to introduce strain to the first channel material. The method further comprises fabricating a first semiconductor device layer on the bulk substrate with the strained first channel material, fabricating a buffer layer comprising dielectric material with a blanket top surface above the first semiconductor layer, bonding to the blanket top surface a bottom surface of a second substrate comprising a buried oxide with a second channel material above the buried oxide, and fabricating a second semiconductor device layer on the second substrate.

What is claimed is: 
     
       1. A method of fabricating a semiconductor structure, the method comprising:
 fabricating, on a bulk substrate having a first strained channel material, a first semiconductor device layer; 
 forming a buffer layer comprising a dielectric material over the first semiconductor device layer; 
 bonding a second substrate to the buffer layer, the second substrate comprising a buried oxide layer and a second strained channel material; and 
 after bonding the second substrate, fabricating a second semiconductor device layer on the second strained channel material, wherein the second strained channel material and the first strained channel material have different chemical compositions. 
 
     
     
       2. The method of  claim 1 , wherein bonding the second substrate comprises bonding the buried oxide layer to the buffer layer such that the buried oxide layer is between the second semiconductor device layer and the buffer layer. 
     
     
       3. The method of  claim 2 , wherein the buffer layer and the buried oxide layer introduce a strain to the second strained channel material. 
     
     
       4. The method of  claim 2 , further comprising:
 before bonding the second substrate, weakening the second strained channel material using an implantation process; and 
 after bonding the second substrate and before fabricating the second semiconductor device layer, reducing a thickness of the second strained channel material by removing a layer of the second strained channel material distal from the bulk substrate. 
 
     
     
       5. The method of  claim 1 , wherein the first strained channel material and the second strained channel material have different types of strains. 
     
     
       6. The method of  claim 5 , wherein the first strained channel material is formed of a first epitaxial material with compressive strain, and the second strained channel material is formed of a second epitaxial material with tensile strain. 
     
     
       7. The method of  claim 6 , wherein fabricating the first semiconductor device layer comprises forming a PMOS transistor on the bulk substrate, and wherein fabricating the second semiconductor device layer comprises forming an NMOS transistor on the second substrate. 
     
     
       8. The method of  claim 6 , wherein the first epitaxial material is germanium or silicon germanium, and the second epitaxial material is silicon. 
     
     
       9. The method of  claim 5 , wherein the first strained channel material is formed of a first epitaxial material with tensile strain, and the second strained channel material is formed of a second epitaxial material with compressive strain. 
     
     
       10. The method of  claim 9 , wherein fabricating the first semiconductor device layer comprises forming an NMOS transistor on the bulk substrate, and wherein fabricating the second semiconductor device layer comprises forming a PMOS transistor on the second substrate. 
     
     
       11. The method of  claim 10 , wherein fabricating the first semiconductor device layer comprises:
 forming a virtual substrate by epitaxially forming a layer of germanium or silicon germanium; and 
 forming the first strained channel material by epitaxially forming a layer of silicon on the virtual substrate. 
 
     
     
       12. A method of fabricating a semiconductor structure, the method comprising:
 growing a first channel material on a bulk substrate, wherein the first channel material has a different chemical composition from a material of the bulk substrate, wherein the first channel material has a first type of strain; 
 forming a first semiconductor device layer on the first channel material, wherein the first semiconductor device layer comprises a first transistor, wherein a channel region of the first transistor comprises the first channel material; 
 forming a buffer layer comprising a dielectric material over the first semiconductor device layer; 
 bonding a second substrate to the buffer layer, wherein the second substrate comprises a second channel material and a buried oxide layer, wherein a first side of the buried oxide layer is bonded to the second channel material, and an opposing second side of the buried oxide layer is bonded to the buffer layer, wherein the second channel material and the first channel material have different chemical compositions; and 
 forming a second semiconductor device layer on the second channel material after bonding the second substrate, wherein the second semiconductor device layer comprises a second transistor, wherein a channel region of the second transistor comprises the second channel material. 
 
     
     
       13. The method of  claim 12 , wherein the buried oxide layer physically contacts the buffer layer. 
     
     
       14. The method of  claim 13 , wherein the first channel material is formed of a first epitaxial material having the first type of strain, wherein the second channel material is formed of a second epitaxial material having a second type of strain different from the first type of strain. 
     
     
       15. The method of  claim 14 , wherein the buffer layer eliminates stress to the first channel material from the buried oxide layer bonded to the buffer layer. 
     
     
       16. The method of  claim 12 , further comprising, after bonding the second substrate and before forming the second semiconductor device layer:
 reducing a thickness of the second channel material. 
 
     
     
       17. A method of fabricating a semiconductor structure, the method comprising:
 fabricating, on a first substrate with a strained first channel material, a first semiconductor device layer; 
 forming a buffer layer on the first semiconductor device layer; 
 forming a buried oxide layer on a second substrate, wherein a first side of the buried oxide layer is in contact with the second substrate; 
 after forming the buried oxide layer, bonding a second side of the buried oxide layer to the buffer layer; 
 reducing a thickness of the second substrate after the bonding; and 
 after reducing the thickness of the second substrate, fabricating a second semiconductor device layer on the second substrate. 
 
     
     
       18. The method of  claim 17 , wherein the second substrate comprises a strained second channel material, wherein a first strain type of the strained first channel material is different from a second strain type of the strained second channel material. 
     
     
       19. The method of  claim 18 , wherein the first semiconductor device layer comprises a first transistor, and the second semiconductor device layer comprises a second transistor, wherein a first channel region of the first transistor comprises the strained first channel material, and a second channel region of the second transistor comprises the strained second channel material. 
     
     
       20. The method of  claim 18 , wherein the strained first channel material is an epitaxial germanium material or an epitaxial silicon germanium material, and the strained second channel material is an epitaxial silicon material.